The system employing an optically encoded digital audio disc (referred to hereafter as a compact disc) is capable of reproducing stereo music of high quality. In such a disc system, if digital data such as data representing characters, display data, or computer program data other than music, or in addition to at least one channel of music can be reproduced without significant change in the structure of a player, then a playback apparatus for visual information such as chart, or statistics by graphics, or picture books of still images, and/or video games could be achieved merely by adding a display device, for example. In this way, the applications of the compact disc system could be extended. The storage capacity of current compact discs is approximately 500M bytes which is advantageously larger than that of conventional flexible discs.
On the other hand, in conventional compact discs, the data is retrieved in relatively large units such as an entire music composition or a passage thereof, since reproduction of audio signals are concerned. It is necessary, however, to read out data in a precise units ranging from 128 bytes to 10K bytes from a a general data storage device.
In the case of music signals, searching accuracy can afford to be relatively low without noticeably affecting the reproduced sound. Therefore,in the conventional reproducing apparatus, audio data of the reproduced signal from the compact disc are once written into a buffer memory so as to be subjected to error correction and to eliminate jitter in the time base. Since a high searching accuracy is not required in a subcoding signal as mentioned above, time base jitter is not eliminated in order to reduce manufacturing costs. Accordingly, there is a problem that if the compact disc is to be used as a data memory, a read address cannot be specified accurately solely by means of the subcoding signal.